べう

びょう · byoo

auxiliary verb 連用形

べう is the masu-stem of べし.

Classical Japanese — you’ll mostly meet it in older texts and set phrases

How it’s built

べしべう

Masu-stem (連用形). The base for ます, たい and ながら, and the way to link two actions: 書き → 書きます.

This spelling is the version with う (sound change, mostly in polite or older speech).

べし is a classical japanese conjugation, so it follows that pattern.